1. Field of the Invention
The present invention relates to an information processing apparatus and an operation method thereof, and more particularly to a technology for securely and continuously performing a data copying process for snapshot difference data while efficiently using storage areas in a copy source and a copy destination.
2. Related Art
One of functions of a storage system is called a snapshot function with which, for a volume in operation (hereinafter, referred to as an “operational volume”), the state at a certain time (hereinafter, the state is referred to as a “snapshot”) is provided to a user in response to a request from the user or the like. This snapshot function is generally implemented in such a way that data (hereinafter, referred to as “difference data”) for reproducing the snapshot of a operational volume at a certain time are saved in advance in a volume (hereinafter, referred to as a “difference volume”) different from the operational volume, and that the snapshot at the certain time is reproduced using the present data of the operational volume and the difference data saved in the difference volume, in response to a request from the user or the like.
Meanwhile, for a certain site such as a data center in which a large amount of data are stored, data duplication has been put into practice in order to reduce or avoid a risk of loosing data due to a disaster or the like. For such data duplication, a different site for providing data storage areas is set up at a place physically distant from the certain site, and the two sites are coupled to each other with a communication network. Then, the data stored in the certain site such as the data center are regularly copied in a storage area in the different site (this data copy process is called a “remote copy” below. In addition, a device or the like on a place where original data are stored is called a “local,” and a device or the like on a place where copied data are stored is called a “remote.”).
The snapshot described first is also subjected to the remote copy process (e.g., refer to Japanese Patent Application Laid-open Publication No. 2007-310631). One of disclosed technologies to securely perform the remote copy of the snapshot is a technology of preventing a capacity shortage of a difference volume for storing difference data in a copy destination (e.g., refer to Japanese Patent Application Laid-open Publication No. 2006-119688).
For example, when a hardware trouble or the like occurs in a system of a local site, a failover process is performed to continue the operation of the system. In the failover process, the system is automatically switched to a system of a remote site in a predetermined procedure. When the snapshot is copied for a remote copy from the local site to the remote site, a problem sometimes occurs that the capacity of a difference volume differs between the local and remote sites. This is because, for example, when a volume being managed by thin-provisioning of hardware is allocated to the difference volume, and when a dynamic allocation of a storage area cannot be made due to a temporary hardware trouble only a storage area on which an allocation has already been made is capable of being used. This problem occurs, for example, in a case where a volume being managed by thin-provisioning of hardware is allocated to the difference volume. More specifically, in this case, if the storage area cannot be dynamically allocated due to a temporary hardware trouble, the difference volume can use only the storage area already allocated, and thereby may face a shortage of the capacity. When such a capacity shortage occurs in the local site, the capacity of the difference volume may differ between the local and remote sites, and result in a failover.
Further, when an operation for improving the use efficiency of a storage system is performed in a local site, e.g., when a management is made in which data stored in a volume with a large amount of unused area is moved to a volume with a smaller capacity, the capacity of a difference volume may become insufficient due to the moving of the data. In this case, also, the capacity of a difference volume may also differ between local and remote sites, and result in a failover.
To cope with such a shortage of the capacity of the difference volume, a non-allocated auxiliary volume is added as the difference volume. However, the capacity of the auxiliary volume may occasionally differ between the local and remote sites. In this case, there is a problem that in one site that has a smaller capacity of an auxiliary volume than the other site, the auxiliary volume cannot be added as the difference volume.
The capacity of an auxiliary volume differs, for example, due to a hardware trouble. Also, when a local site and a remote site are independently managed and separately undergo addition or the like of volumes, the number of auxiliary volumes may differ between the two sites.
Against this background, the present invention aims to provide an information processing apparatus and an operation method thereof for securely and continuously perform a data copying process for snapshot difference data while efficiently using storage areas in a copy source and a copy destination.